Hoist chains or lifting chains are commonly used with hoist devices and cranes for lifting loads. There are various types of hooks which can be attached to these chains such as hoisting or lifting hooks, shortening hooks and sling hooks.
Lifting hooks comprise a substantially arcuate hook or u-shaped hook and are usually equipped with a slip-prevention device such as a safety latch, to prevent the disengagement of the hoist chain, wire rope sling or rope to which a load is attached. However, in the event that the slip-prevention device fails, the chain can escape from the hook.
Shortening hooks are commonly used in chain suspension systems which can have several chains. The shortening hooks generally comprise an open u-shaped hook for receiving a chain link at one end and a pin-hole cable connection at an opposing end for receiving a connection to a load. However, as a load is raised and lowered the chain link can move on the hook and escape from the hook. Various modifications have been made to alter the design of these types of hooks to limit the likelihood of movement of the chain and for specific applications. However, in certain circumstances it is still be possible for the chain link engaged in the hook to slip from the hook and escape.
In this specification, the terms “comprises”, “comprising” or similar terms are intended to mean a non-exclusive inclusion, such that a method and/or apparatus that comprises a list of elements does not include those elements solely, but may well include other elements not listed.